The invention is in the field of electrical circuit control and protection. More specifically it relates to an operator which controls a circuit breaker by rapidly closing it against the force of the breaker's opening mechanism and keeping the breaker closed but, when needed, permitting the circuit breaker's opening mechanism to rapidly open the circuit breaker in order to disconnect a load from a power source.
In normal circuit operation, circuit breakers can serve to energize and deenergize loads while under abnormal conditions, such as electrical shorts or sustained overloads, they can be used to rapidly deenergize the load and thus protect equipment and the surroundings from possible damage. Particularly at higher power levels, such as in the case of the SP brand power breakers available from Siemens Energy and Automation, Inc., which are rated for 15 KV to 72 V and 40 KA, it is desirable to achieve very rapid circuit breaker opening and closing in order to reduce undesirable electrical transients. For rapid opening of an electro-mechanical circuit breaker using internal springs, such as in said SP brand, the internal springs of the circuit breaker must be sufficiently powerful. For rapid closing, the bias of these internal springs must be overcome positively and rapidly. A mechanism called an operator can be used to rapidly close one or more interrupters (contacts) against the force of opening springs which are a part of the breaker and to permit rapid opening of the interrupters.
Different types of such operators have been proposed, including examples which use springs to store energy that can be rapidly released to close a circuit breaker and examples which use pneumatic mechanisms. An example of a pneumatic operator is available from Siemens Energy and Automation, Inc. under the designation Pneumatic Operator Mechanism SA-7. While known operators have many desirable features, it is believed that a need still remains for an improved operator having high reliability and functionality and an improved balance of other characteristics. This invention is directed to meeting such a need.
An exemplary spring-powered operator embodying the invention controls a circuit breaker having an opening mechanism which is charged when the breaker closes and which when allowed to discharge opens the circuit breaker. This opening mechanism can be internal springs of a circuit breaker such as a breaker carrying said SP brand. The operator has a lever coupled with the circuit breaker's opening mechanism and constrained to move between an open position at which the circuit breaker is open and a closed position at which the circuit breaker is closed. A first charge command is provided when the lever is at its open position and therefore the circuit breaker is open. In response to this first charge command, the operator charges an energy storing spring, e.g., compresses the spring, and latches the spring at its charged position. When it is time to close the circuit breaker, a discharge command is provided and, in response, the operator unlatches the spring and allows it to discharge. The operator uses the energy released by the discharging spring to rotate a cam that engages the lever coupled to the circuit breaker and moves that lever from its open to its closed position to thereby close the circuit breaker, and latches the lever at its closed position to thereby keep the circuit breaker closed. This discharging of the spring also generates a second charge command and, in response, the operator again starts charging the energy storing spring and then latches it in its charged position. If and when a trip signal is received, i.e., when the circuit breaker should be opened, the operator unlatches the lever from its latched position to thereby allow the circuit breaker's opening mechanism, e.g., the breaker's internal springs, to open the circuit breaker. Because the operator has charged immediately after closing the circuit breaker, it is ready to immediately respond to a discharge command and again close the circuit breaker.
In the disclosed example of the invention, the operator charges itself by using an electric motor to indirectly drive a ratchet wheel which in turn indirectly rotates a crank pulling a rod that compresses the energy storing spring to its charged position. To discharge, the operator releases the spring and the expanding spring rotates the crank through the same rod. This crank rotation in turn rotates the cam which strikes the lever connected through a linkage to the circuit breaker, e.g., to the breaker's interrupters, to move the interrupters against the force of the circuit breaker's opening mechanism, e.g., opening springs, and to thereby rapidly and safely close the circuit breaker. The sequence for the operator is: charge, discharge to close the circuit breaker, and immediately charge again to be ready for the next closing of the circuit breaker. The operator allows the circuit breaker to open at any time. The disclosed embodiments of the invention use a particularly low number of parts and relatively simple components and interaction of components, which is believed to improve reliability, and are believed to be particularly effective in achieving a rapid and positive closing of circuit breakers in high power circuits and in allowing rapid opening of such circuit breakers.